We identify an axis connecting two opposite ‘ears’ in the supernova remnant W49B and morphological signatures of three arcs around this axis that we claim are sections of full circum-jet rings. Based on recent identifications of morphological signatures of jets in core-collapse supernovae (CCSNe), including ejecta-rich axes, we re-examine images of W49B and identify a heavy element-rich protrusion (ear) as a jet-inflated structure. We identify the opposite ear and a clump at its tip as the signature of the opposite jets. The line connecting the two clumps at the tips of the two opposite ears forms the main jet axis of W49B. We compare the three arcs around the main jet axis in W49B to the circum-jet rings of the jets in the Cygnus A galaxy and deduce that these arcs are sections of full circum-jet rings in W49B. In W49B, the jets are long gone, as in some planetary nebulae with circum-jet rings. Identifying the main jet axis is incompatible with a type Ia supernova. It leaves two possibilities: that jets exploded W49B as a CCSN, i.e. the jittering jets explosion mechanism where the pair of jets we identify is one of many that exploded the star, or that the explosion was a common envelope jet supernova with a thermonuclear outburst, i.e. both the pair of jets and thermonuclear outburst exploded the core of a red supergiant star as a pre-existing neutron star tidally destroyed it.

We study the late-time evolution of the compact Type IIb SN 2001ig in the spiral galaxy NGC 7424, with new and unpublished archival data from the Australia Telescope Compact Array and the Australian Square Kilometre Array Pathfinder. More than two decades after the SN explosion, its radio luminosity is showing a substantial re-brightening: it is now two orders of magnitude brighter than expected from the standard model of a shock expanding into a uniform circumstellar wind (i.e. with a density scaling as $R^{-2}$). This suggests that the SN ejecta have reached a denser shell, perhaps compressed by the fast wind of the Wolf–Rayet progenitor or expelled centuries before the final stellar collapse. We model the system parameters (circumstellar density profile, shock velocity, and mass loss rate), finding that the denser layer was encountered when the shock reached a distance of $\approx 0.1$ pc; the mass-loss rate of the progenitor immediately before the explosion was $\dot{M}/v_{w} \sim 10^{-7} {\rm M}_\odot {\mathrm {~yr}}^{-1} {\mathrm {km}}^{-1} {\mathrm {s}}$. We compare SN 2001ig with other SNe that have shown late-time re-brightenings, and highlight the opposite behaviour of some extended Type IIb SNe which show instead a late-time flux cut-off.

We present the results of a detailed high-resolution spectroscopic analysis (SUBARU/HDS spectra, R$\sim$50 000) of three faint high-latitude carbon stars HE 1104$-$0957, HE 1205$-$0521, and HE 1244$-$3036. Our estimated metallicity for these objects is $-$2.96, $-$2.63, and $-$2.49, respectively. The surface chemical compositions of the objects are found to be characterised by enhanced carbon and heavy elements, such as Y, Ba, La, and Ce. Using the classification criteria for carbon-enhanced metal-poor (CEMP) stars the objects HE 1104$-$0957 and HE 1205$-$0521 could not be classified into any known CEMP sub-classes, whereas the object HE 1244$-$3036 is found to be likely a CEMP-s star. The observed abundance patterns in HE 1244$-$3036 are also found to match well with the yields of a 2 M$_{\odot}$ AGB star with [Fe/H] = $-$2.50. Although our kinematic analysis indicates that the objects belong to the halo population, the elemental abundance ratios of HE 1104$-$0957 and HE 1205$-$0521 do not match well with those of typical halo objects. Estimated elemental abundances are presented, and kinematic properties of the stars are discussed.

Advancements in VLBI instrumentation, driven by the geodetic community’s goal of achieving positioning accuracy of 1 mm and stability of 0.1 mm/y, have led to the development of new broadband systems. Here, we assess the potential of these new capabilities for space weather monitoring. These enhanced VLBI capabilities were used to investigate interplanetary scintillation (IPS), a phenomenon caused by the scattering of radio waves due to density irregularities in the solar wind. Compact radio sources near the Sun were observed using the AuScope VLBI array in Australia, which consists of 12-m telescopes at Hobart, Katherine, and Yarragadee. The baseline lengths between these telescopes are approximately 3 400 km (Hobart–Katherine), 3 200 km (Hobart–Yarragadee), and 2 400 km (Katherine–Yarragadee). The observations covered solar elongations from 6.5$^\circ$ to 11.3$^\circ$ and frequencies between 3 and 13 GHz. The study focused on phase scintillation as an indicator of turbulence in the solar wind. As the solar elongation decreased, we observed an increase in the phase scintillation index, consistent with theoretical models. Importantly, the broadband system also detected IPS using relatively weak radio sources. Additionally, the phase scintillation increased with baseline length, in agreement with Kolmogorov turbulence with an index of 11/3. These findings demonstrate the effectiveness of geodetic broadband VLBI in capturing detailed features of the solar wind. This capability enables continuous space weather monitoring and advances our understanding of solar and interplanetary dynamics.

The radio telescopes of the European VLBI Network (EVN) and the University of Tasmania (UTAS) conducted an extensive observation campaign of the European Space Agency’s (ESA) Mars Express (MEX) spacecraft between 2013 and 2020. The campaign, carried out under the Planetary Radio Interferometry and Doppler Experiment (PRIDE) framework, aimed to study interplanetary phase scintillation and assess the noise budget in the closed-loop Doppler observations. The average closed-loop Doppler noise was determined to be approximately 10 mHz at a 10-s integration time, reaffirming the technique’s suitability for radio science experiments. We evaluated how different observational parameters such as the solar elongation, antenna size, and elevation angle impact the Doppler noise. A key part of the analysis involved comparing results from co-located telescopes to investigate system noise effects. Co-located telescopes at both Wettzell and Hobart provided highly consistent results, with any deviations serving as diagnostic tools to identify station-dependent issues. Additionally, the use of phase calibration tones during spacecraft tracking showed that the instrumental noise contribution is of the order of 5$\%$ of the total noise. This study provides a detailed noise budget for closed-loop Doppler observations with VLBI telescopes while emphasizing the effectiveness of the co-location method in isolating system-level noise. These findings are important for optimizing future radio science and VLBI tracking missions using stations outside the the Deep Space Network (DSN) and European Space Tracking (ESTRACK) network.

The Lyman alpha (Ly$\alpha$) forest in the spectra of $z\gt5$ quasars provides a powerful probe of the late stages of the epoch of reionisation (EoR). With the recent advent of exquisite datasets such as XQR-30, many models have struggled to reproduce the observed large-scale fluctuations in the Ly$\alpha$ opacity. Here we introduce a Bayesian analysis framework that forward-models large-scale lightcones of intergalactic medium (IGM) properties and accounts for unresolved sub-structure in the Ly$\alpha$ opacity by calibrating to higher-resolution hydrodynamic simulations. Our models directly connect physically intuitive galaxy properties with the corresponding IGM evolution, without having to tune ‘effective’ parameters or calibrate out the mean transmission. The forest data, in combination with UV luminosity functions and the CMB optical depth, are able to constrain global IGM properties at percent level precision in our fiducial model. Unlike many other works, we recover the forest observations without invoking a rapid drop in the ionising emissivity from $z\sim7$ to 5.5, which we attribute to our sub-grid model for recombinations. In this fiducial model, reionisation ends at $z=5.44\pm0.02$ and the EoR mid-point is at $z=7.7\pm0.1$. The ionising escape fraction increases towards faint galaxies, showing a mild redshift evolution at fixed UV magnitude, $M_\textrm{UV}$. Half of the ionising photons are provided by galaxies fainter than $M_\textrm{UV} \sim -12$, well below direct detection limits of optical/NIR instruments including $\textit{ JWST}$. We also show results from an alternative galaxy model that does not allow for a redshift evolution in the ionising escape fraction. Despite being decisively disfavoured by the Bayesian evidence, the posterior of this model is in qualitative agreement with that from our fiducial model. We caution, however, that our conclusions regarding the early stages of the EoR and which sources reionised the Universe are more model-dependent.

Interstellar hydrogen atoms (H atoms) penetrate into the heliosphere through the region of the solar wind interaction with the interstellar plasma due to their large mean free path. Resonant charge exchange of H atoms with protons has been considered as the main interaction process between the components. In the majority of models, other processes like elastic H-H and H-p collisions are not included. Moreover, it has been assumed that the velocities of the colliding particles remain unchanged during charge exchange. This corresponds to the scattering on the angle of $\pi$ in the centre mass rest frame. The goal of this paper is to explore effects of the elastic H-H and H-p collisions as well as the angular scattering during charge exchange on the distribution of the interstellar atoms in the heliosphere and at its boundary. We present results of simple (and therefore, easily repeatable) kinetic model of the interstellar atom penetration through the region of the solar and interstellar winds interaction into the heliosphere. As a result of the model, we compute the distribution function of the interstellar atoms at different heliospheric distances. Further, this distribution function is used to compute its moments and potentially observable features such as absorption and backscattered spectra in the Lyman-alpha line. Results show that there are differences in the behaviour of the distribution function when considering elastic collisions and the changes in the moments of the distribution achieve 10%. Therefore, in cases where precise calculation of H atom parameters is essential, such as in the modelling of backscattered Lyman-$\alpha$ emission, elastic collisions must be considered.

In this work, we studied the broadband temporal and spectral properties of the flat-spectrum radio quasar Ton 599. We collected the long-term data from January 2019 to August 2024 when the source was in a long flaring episode. We used the Bayesian block methodology to identify the various flux states, including three flares. The broadband fractional variability is estimated during two flaring states. The F$_{\text{var}}$ variation with respect to frequency shows a nearly double hump structure similar to broadband SED. The power spectral density shows a pink-noise kind of stochastic variability in the light curve, and we do not see any break in the power spectrum, suggesting a much longer characteristic timescale is involved in gamma-ray variability. The flux distribution is well-fitted with a double log-normal flux distribution, suggesting the variability of non-linear in nature. The gamma-ray, optical, and X-ray emissions were found to be highly correlated with a zero time lag, suggesting a co-spatial origin of their emissions. We used the one-zone leptonic model to reproduce the broadband spectrum in the energy range from the IR to very high-energy gamma rays. The increase in the magnetic field and the Doppler factor were found to be the main causes for high flux states. The XMM-Newton spectra taken during one of the flaring durations exhibit a signature of thermal black body emission from the accretion disc, suggesting a possible disc-jet coupling. This has also been indicated by the gamma-ray flux distribution, which shows the distribution as non-linear in nature, which is mostly seen in galactic X-ray binaries or active galactic nuclei, where the accretion disc dominates the emission.

Spectra have been obtained with the multi-fibre instrument 2dF on the Anglo-Australian Telescope of 89 candidate main sequence stars in the globular cluster M55 (NGC 6809). Radial velocities and Gaia proper motions confirm 72 candidates as cluster members. Among these stars one stands out as having a substantially stronger G-band (CH) than the rest of the member sample. The star is a dwarf carbon star that most likely acquired the high carbon abundance ([C/Fe] $\approx$ 1.2 $\pm$ 0.2) via mass transfer from a $\sim$1$-$3 M$_{\odot}$ binary companion (now a white dwarf) during its AGB phase of evolution. Interestingly, M55 also contains a CH-star that lies on the cluster red giant branch – the low central concentration/low density of this cluster presumably allows the survival of binaries that would otherwise be disrupted in denser systems. The existence of carbon stars in six other globular clusters is consistent with this hypothesis, while the origin of the carbon-enhanced star in M15 (NGC 7078) is attributed to a merger process similar to that proposed for the origin of the carbon-rich R stars.

Brown dwarfs are failed stars with very low mass (13–75 Jupiter mass) and an effective temperature lower than 2 500 K. Their mass range is between Jupiter and red dwarfs. Thus, they play a key role in understanding the gap in the mass function between stars and planets. However, due to their faint nature, previous searches are inevitably limited to the solar neighbourhood (20 pc). To improve our knowledge of the low mass part of the initial stellar mass function and the star formation history of the Milky Way, it is crucial to find more distant brown dwarfs. Using James Webb Space Telescope (JWST) COSMOS-Web data, this study seeks to enhance our comprehension of the physical characteristics of brown dwarfs situated at a distance of kpc scale. The exceptional sensitivity of the JWST enables the detection of brown dwarfs that are up to 100 times more distant than those discovered in the earlier all-sky infrared surveys. The large area coverage of the JWST COSMOS-Web survey allows us to find more distant brown dwarfs than earlier JWST studies with smaller area coverages. To capture prominent water absorption features around 2.7 ${\unicode{x03BC}}$m, we apply two colour criteria, $\text{F115W}-\text{F277W}+1\lt\text{F277W}-\text{F444W}$ and $\text{F277W}-\text{F444W}\gt\,0.9$. We then select point sources by CLASS_STAR, FLUX_RADIUS, and SPREAD_MODEL criteria. Faint sources are visually checked to exclude possibly extended sources. We conduct SED fitting and MCMC simulations to determine their physical properties and associated uncertainties. Our search reveals 25 T-dwarf candidates and 2 Y-dwarf candidates, more than any previous JWST brown dwarf searches. They are located from 0.3 to 4 kpc away from the Earth. The spatial number density of 900–1 050 K dwarf is $(2.0\pm0.9) \times10^{-6}\text{ pc}^{-3}$, 1 050–1 200 K dwarf is $(1.2\pm0.7) \times10^{-6}\text{ pc}^{-3}$, and 1 200–1 350 K dwarf is $(4.4\pm1.3) \times10^{-6}\text{ pc}^{-3}$. The cumulative number count of our brown dwarf candidates is consistent with the prediction from a standard double exponential model. Three of our brown dwarf candidates were detected by HST, with transverse velocities $12\pm5$, $12\pm4$, and $17\pm6$ km s$^{-1}$. Along with earlier studies, the JWST has opened a new window of brown dwarf research in the Milky Way thick disk and halo.

Interactions play a significant role in the formation and evolution of galaxies in the Universe. The galaxy systems, NGC 7252 and NGC 5291, are two nearby interacting systems that are hosting tidal dwarf galaxies (TDGs) and star-forming knots. The present work aims (a) to determine the attenuation-corrected star formation rate (SFR) of the interacting system NGC 7252, (b) to compare the star formation in the NGC 7252 system with that of the NGC 5291 system, and (c) to explore the relation between surface densities of gas and SFR in these two systems. The study utilises high-resolution FUV and NUV imaging data from the ultraviolet imaging telescope on board AstroSat. Six star-forming regions, including the merger remnant, were identified in the NGC 7252 system. The SFR corrected for attenuation of the knots in the NGC 7252 system is determined using the continuum slope $\beta$ calculated from the FUV-NUV colour. It has been observed that the attenuation-corrected SFR values of the knots in this system fall within the range of SFR values determined for the NGC 5291 knots. The TDGs in both systems adhere to the same Kennicutt–Schmidt relation as regular spiral galaxies.

Obscuration in active galactic nuclei (AGN) provides valuable insights into the nature of the material surrounding the central engine. Compton-thick AGN (CTAGN), characterised by a column density of $N_{\mathrm{H}} \geq 1.5 \times 10^{24} \ \mathrm{cm}^{-2}$, are heavily obscured by substantial amounts of dust and gas. While X-ray observations are primarily used to determine this column density, our understanding of obscuration properties in the sub-mm regime, particularly for CTAGN, remains limited. In this study, we analyse archival data from the Atacama Large Millimetre/sub-millimetre Array (ALMA) for both CTAGN and non-CTAGN sources, as identified by the 70-month catalogue of the all-sky hard X-ray Swift/Burst Alert Monitor survey and other X-ray surveys. Integrated intensity maps (moment 0) of CO(3–2) emission reveal a concentrated distribution of dense gas around the nucleus. Utilising a constant CO-to-H2 conversion factor, $X_{\mathrm{CO}} = 2.2 \times 10^{20} \ \mathrm{cm}^{-2} \ (\mathrm{K\ km\ s}^{-1})^{-1}$, we find that the derived molecular hydrogen column densities, $N_{\mathrm{H_2}}$, are generally lower than the total hydrogen column densities, $N_{\mathrm{H}}$, obtained from X-ray observations. However, the $N_{\mathrm{H_2}}$ values derived in this work are slightly higher than those reported in previous studies due to the adoption of a higher CO-to-H2 conversion factor. This discrepancy between $N_{\mathrm{H}}$ and $N_{\mathrm{H_2}}$ is consistent with prior findings that X-ray-derived column densities are typically higher, except in the case of non-CTAGN, where $N_{\mathrm{H_2}}$ can exceed $N_{\mathrm{H}}$. Statistical analysis using Kendall and Spearman tests reveals a positive monotonic relationship between $N_{\mathrm{H}}$ and $N_{\mathrm{H_2}}$, although the correlation is not statistically significant. This suggests a complex interplay of factors influencing these properties. The optically thick nature of CO in dense regions may contribute to the observed discrepancies. Our results highlight the importance of adopting an accurate CO-to-H2 conversion factor to derive reliable column densities, which could serve as an alternative method for identifying CTAGN. Further investigations with more comprehensive data sets and refined methodologies are needed to better understand the relationship between sub-millimetre and X-ray properties in AGNs.

The effects of diffraction, reflection, and mutual coupling on the spectral smoothness of radio telescopes become increasingly important at low frequencies, where the observing wavelength may be significant compared with the antenna or array dimensions. These effects are important for both traditional parabolic antennas, which are prone to the ‘standing wave’ phenomenon caused by interference between direct and scattered wavefronts, and aperture arrays, such as the SKA-Low, MWA, HERA, and LOFAR which have more complicated scattering geometries and added dependence on pointing direction (scan angle). Electromagnetic modelling of these effects is computationally intensive and often only possible at coarse frequency resolution. Therefore, using the example of SKA-Low station configurations, we investigate the feasibility of parameterising scattering matrices and separating antenna and array contributions to telescope chromaticity. This allows deeper insights into the effect on spectral smoothness and frequency-dependent beam patterns of differing antenna configurations. Even for the complicated SKA-Low element design, band-limited delay-space techniques appear to produce similar results to brute-force electromagnetic models and allow for faster computation of station beam hypercubes (position, frequency, and polarisation-dependent point spread functions) at arbitrary spectral resolution. As such techniques could facilitate improvements in the design of low-frequency spectral-line surveys, we conduct a simulated Cosmic Dawn experiment using different observing techniques and station configurations.

Polar ring galaxies (PRGs) are a unique class of galaxies characterised by a ring of gas and stars orbiting nearly orthogonal to the main body. This study delves into the evolutionary trajectory of PRGs using the exemplary trio of NGC 3718, NGC 2685, and NGC 4262. We investigate the distinct features of PRGs by analysing their ring and host components to reveal their unique characteristics through spectral energy distribution (SED) fitting. Using CIGALE, we performed SED fitting to independently analyse the ring and host spatially resolved regions, marking the first decomposed SED analysis for PRGs, which examines stellar populations using high-resolution observations from AstroSat UVIT at a resolved scale. The UV-optical surface profiles provide an initial idea that distinct patterns in the galaxies, with differences in FUV and NUV, suggest three distinct stages of ring evolution in the selected galaxies. The study of resolved-scale stellar regions reveals that the ring regions are generally younger than their host galaxies, with the age disparity progressively decreasing along the evolutionary sequence from NGC 3718 to NGC 4262. Star formation rates (SFR) also exhibit a consistent pattern, with higher SFR in the ring of NGC 3718 compared to the others, and a progressive decrease through NGC 2685 and NGC 4262. Finally, the representation of the galaxies in the HI gas fraction versus the NUV–$\text r$ plane supports the idea that they are in three different evolutionary stages of PRG evolution, with NGC 3718 in the initial stage, NGC 2685 in the intermediate stage, and NGC 4262 representing the final stage. This study concludes that PRGs undergo various evolutionary stages, as evidenced by the observed features in the ring and host components. NGC 3718, NGC 2685, and NGC 4262 represent different stages of this evolution, highlighting the dynamic nature of PRGs and emphasising the importance of studying their evolutionary processes to gain insights into galactic formation and evolution.

AstroSat observed transient neutron star low-mass X-ray binary XTE J1701-462 for a total duration of $\sim$ 135 ks during its 2022 outburst. We report the results of a detailed spectral and timing analysis carried out using this data. The source traced a complete ‘Z’ shaped structure in the hardness intensity diagram (HID). The source exhibited an extended horizontal branch and a short-dipping flaring branch in the HID. The spectra of the source were fitted with different approaches. We find that most suitable spectral model comprises emission from a standard multi-color accretion disk (diskbb in XSPEC) and Comptonised radiation from a hot central corona, described by Comptb model of XSPEC. The observed disk component is cool, having a temperature in the range of $\sim 0.28-0.42$ keV and truncated far ($\sim$ 250 - 1600 km) from the compact object. The Compton corona has an optical depth in the range of $\sim 3.4- 5.1 $ and a temperature in the range of $3.3-4.5$ keV. The disk and corona flux as well as truncation radius vary significantly along the HID. The temperature $kT_{in}$ depends on both luminosity and inner disk radius and hence shows marginal variation as compared to the truncation radius. We discuss possible scenarios to explain the relationship between the spectral evolution and motion of the source along the HID. The timing analysis revealed horizontal branch oscillations (HBOs) in the frequency range $\sim 34-40$ Hz. The frequency and rms strength of HBO vary systematically as the source moves along the horizontal branch (HB). The observed correlation of the HBO properties with the position on the HB is similar to that previously reported in this source using RXTE data during the 2006 outburst of the source. The source also showed normal branch oscillations (NBOs) with frequency $\sim$ 6.7 Hz in the middle and the lower normal branch. The energy-dependent study of the HBO properties suggests that the HBO is stronger in the higher energy band. We also observed very-low frequency noise and band-limited noise (BLN) components in the power density spectra. The break frequency of BLN component was found to be tightly correlated with the HBO frequency. We discuss possible models to explain the origin and nature of the observed features in the PDS.

The cosmic 21 cm signal serves as a crucial probe for studying the evolutionary history of the Universe. However, detecting the 21 cm signal poses significant challenges due to its extremely faint nature. To mitigate the interference from the Earth’s radio frequency interference (RFI), the ground and the ionospheric effects, the Discovering the Sky at the Longest Wavelength (DSL) project will deploy a constellation of satellites in lunar orbit, with its high-frequency daughter satellite tasked with detecting the global 21 cm signal from cosmic dawn and reionization era (CD/EoR). We intend to employ the vari-zeroth-order polynomial (VZOP) for foreground fitting and subtracting. We have studied the effect of thermal noise, thermal radiation from the Moon, the lunar reflection, anisotropic frequency-dependent beam, inaccurate antenna beam pattern, and RFI contamination. We discovered that the RFI contamination can significantly affect the fitting process and thus prevent us from detecting the signal. Therefore, experimenting on the far side of the moon is crucial. We also discovered that using VZOP together with DSL, after 1080 orbits around the Moon, which takes about 103 days, we can successfully detect the CD/EoR 21 cm signal.

The stellar age and mass of galaxies have been suggested as the primary determinants for the dynamical state of galaxies, with environment seemingly playing no or only a very minor role. We use a sample of 77 galaxies at intermediate redshift ($z\sim0.3$) in the Middle-Ages Galaxies Properties with Integral field spectroscopy (MAGPI) Survey to study the subtle impact of environment on galaxy dynamics. We use a combination of statistical techniques (simple and partial correlations and principal component analysis) to isolate the contribution of environment on galaxy dynamics, while explicitly accounting for known factors such as stellar age, star formation histories, and stellar masses. We consider these dynamical parameters: high-order kinematics of the line-of-sight velocity distribution (parametrised by the Gauss-Hermite coefficients $h_3$ and $h_4$), kinematic asymmetries $V_{\textrm{asym}}$ derived using kinemetry, and the observational spin parameter proxy $\lambda_{R_e}$. Of these, the mean $h_4$ is the only parameter found to have a significant correlation with environment as parametrised by group dynamical mass. This correlation exists even after accounting for age and stellar mass trends. We also find that satellite and central galaxies exhibit distinct dynamical behaviours, suggesting they are dynamically distinct classes. Finally, we confirm that variations in the spin parameter $\lambda_{R_e}$ are most strongly (anti-)correlated with age as seen in local studies, and show that this dependence is well-established by $z\sim0.3$.

We present a chemo-dynamical study conducted with 2dF$+$AAOmega of $\sim 6\,000$ Gaia DR3 non-variable candidate metal-poor stars that lie in the direction of the Galactic plane. Our spectral analysis reveals 15 new extremely metal-poor (EMP) stars, with the lowest metallicity at $\left[\text{Fe/H}\right] = -4.0 \pm 0.2$ dex. Two of the EMP stars are also carbon enhanced, with the largest enhancement of $\left[\text{C/Fe}\right] = 1.3 \pm 0.1$ occurring in a dwarf. Using our $\left[\text{C/Fe}\right]$ results, we demonstrate that the number of carbon-depleted stars decreases with lower metallicities, and the fraction of carbon-enhanced stars increases, in agreement with previous studies. Our dynamical analysis reveals that the fraction of prograde and retrograde disk stars, defined as $z_{\mathrm{max}} \lt 3$ kpc, with $J_{\phi}/J_{\mathrm{tot}} \gt 0.75$ and $J_{\phi}/J_{\mathrm{tot}} \lt -0.75$, respectively, changes as metallicities decrease. Disk stars on retrograde orbits make up $\sim 10$% of all the stars in our sample with metallicities below $-2.1$ dex. Interestingly, the portion of retrograde disk stars compared with the number of kinematically classified halo stars is approximately constant at $4.6$% for all metallicities below $-1.5$ dex. We also see that $J_{\phi}$ increases from $380 \pm 50$ to $1320 \pm 90$ km s$^{-1}$ kpc across metallicity range $-1.5$ to $-1.1$, consistent with the spin-up of the Galactic disk. Over the metallicity range $-3.0 \lt \left[\text{Fe/H}\right] \lt -2.0$, the slopes of the metallicity distribution functions for the prograde and retrograde disk stars are similar and comparable to that for the halo population. However, detailed chemical analyses based on high-resolution spectra are needed to distinguish the accreted versus in situ contributions. Finally, we show that our spectroscopic parameters reveal serious systematics in the metallicities published in recent studies that apply various machine learning techniques to Gaia XP spectra.

Current and future surveys rely on machine learning classification to obtain large and complete samples of transients. Many of these algorithms are restricted by training samples that contain a limited number of spectroscopically confirmed events. Here, we present the first real-time application of Active Learning to optimise spectroscopic follow-up with the goal of improving training sets of early type Ia supernovae (SNe Ia) classifiers. Using a photometric classifier for early SN Ia, we apply an Active Learning strategy for follow-up optimisation using the real-time Fink broker processing of the ZTF public stream. We perform follow-up observations at the ANU 2.3m telescope in Australia and obtain 92 spectroscopic classified events that are incorporated in our training set. We show that our follow-up strategy yields a training set that, with 25% less spectra, improves classification metrics when compared to publicly reported spectra. Our strategy selects in average fainter events and, not only supernovae types, but also microlensing events and flaring stars which are usually not incorporated on training sets. Our results confirm the effectiveness of active learning strategies to construct optimal training samples for astronomical classifiers. With the Rubin Observatory LSST soon online, we propose improvements to obtain earlier candidates and optimise follow-up. This work paves the way to the deployment of real-time AL follow-up strategies in the era of large surveys.